The invention relates generally to the field of optics, and in particular to reflective optical elements in optical systems such as telescopes. More specifically, the invention relates to the design of lightweight reflective optical elements.
Lightweight optical mirrors used for focusing light rays in optical systems such as telescopes are well known. One approach to achieving light weight in such mirrors is to provide a honeycomb core structure behind the reflective optical surface of the mirror. See, for example, U.S. Pat. No. 3,644,022 issued Feb. 22, 1972, to Jagdt et al. which shows a lightweight optical element having a honeycomb support structure fused to the back of a relatively thin front plate. The honeycomb structure has walls extending generally perpendicular to the optical surface of the front plate. A major shortcoming of this type of construction is that it is relatively high cost and includes the assembly of a number of precision parts. The construction process may be subject to difficulty during the thermal heating and cooling cycles employed to fuse the mirror components, resulting in incomplete joining of the components and residual thermal stresses. The thermal cycles may also change the thermal properties of the mirror elements, resulting in loss of thermal stability during use of the finished mirror. Furthermore, the conventional lightweight mirror manufacturing methods require relatively long lead time for the elements of the mirror.
There is a need therefore for an improved mirror structure that avoids the problems noted above with respect to prior art lightweight mirror structures.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a lightweight mirror structure is formed from a unitary body of mirror blank material by using an abrasive water jet cutting apparatus to cut a plurality of cylindrical channels in the blank between and extending parallel to the mirror surface and the back surface of the mirror structure. The process may be employed to quickly produce inexpensive lightweight mirror structures.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
The present invention has the advantages of being able to rapidly produce a lightweight mirror structure in a fraction of the time at a fraction of the cost of the prior art methods. The method uses only a single piece of starting material and therefore avoids the materials handling costs of the prior art methods employing multi-piece constructions. The resulting mirror structure is relatively free from manufacturing induced stresses without the need for annealing cycles, and is structurally sound due to the unitary construction.